Stabilized gasoline-soluble disazo dye compositions and process of preparing same



llnited States Patent assignor to E. I. du Del., a

This invention is directed to novel stable disazo dye compositions and aprocess for preparing these freefiowing, storage-stable, red disazo dyepowder compositions which are useful in coloring gasoline. In moderngasoline refineries, the dyes used for coloring the gasoline are oftenadded through eduction pipes. This method makes it essential that thedye powders are free-flowing, meaning that they must not cake uponstorage, as is the tendency, particularly in hot warehouses.

The inventor faced the problem of determining the cause of caking indisazo red dye powders used for coloring gasoline. Once the caking onstorage was discovered to be associated with the change from an unstablecrystalline form to a stable crystalline form, the problem was one ofproducing the stable form directly in manufacture. Associated with themain problem of storage stability were the usual requirements of shade,strength, solubility in gasoline, and free-flowing properties. The dyesused must dissolve at least to the extent of 0.25 to 0.40 milligram in100 ml. of isooctane (the usual concentration in the gasoline beforesale), if the refiner educts dye directly into the gasoline, andpreferably to the extent of 100 to 500 milligrams in 100 ml. ofisooctane when the refiner educts or pours dye powder into a solvent toprepare a concentrated solution, latter added to the final gasoline.

it is an object of the present invention to provide novel stable disazodye compositions and a process for preparing these disazo dye powdercompositions, the dye powders of which do not cake on storage and aresuitable for coloring gasoline stocks. A further object is to change atleast of the polymorphic dye powders in a dye mixture to the beta formby heating at about 80 C. or higher as more fully described herein.These and other objects will become apparent in the followingdescription and claims.

is to be understood that by the terms alpha and beta is meant the one ormore metastable alpha crystal forms and the stable beta crystal form.These terms do no imply that the stable beta crystal form of onepolymorphic dye has the same crystal lattice as the beta form of adifierent polymorphic dye. For instance, the beta or stable crystal ofSudan 1V (1-(4-o-tolylazo-otolylazo) -2-naphthol) is in the form ofneedles; the alpha i and alpha ll forms of Sudan HI(l-(p-phenylazophenylazo)-2-naphthol) are also needles while its stablebeta form is in a different crystal lattice.

More specifically, the present invention is directed to novel stabledisazo dye compositions and processes for their manufacture whereby asoft, free-flowing disazo dye powder, stabilized against caking due tochange in crystal phase during storage, is prepared from an unstablecrystalline form of a dye of the group (a)l-(pphenylazo-phenylazo)-2-naphthol, (b)l-(4-o-tolylazo-otolylazo)-2-naphthol, (c) l-(4-phenylazo-2,5-xylylazo)-2 naphthol, (d) l-(4 o tolylazo-2,5 -xylylazo)-2- naphthol, and (e)1-[4-(2,4-xylylazo)-2,5-xylylazo]-2- naphthol, or any mixture of thesedyes, by heating said dyes, under selected wet or dry conditions, atabout 80 to 100 C. until at least 5% by weight of the product isconverted to the stable beta crystalline form. When the dye is heated inan aqueous slurry, the heating step stabilized dye.

is followed by filtering, washing, drying and grinding the Thestabilization process may be conducted in the presence of anonpolymorphic isomer or homolog of the polymorphic dyes, the amount ofthe polymorphic type being at least 30% of dyes in the mixture; thestabilizations may also be conducted in the presence of an inert,colorless resin in an amount which does not exceed 35% of the dyeweight.

It is not necessary to convert more than a part of the polymorphic dyeto beta form by the method of this invention, since a small amount inbeta form, as described, is sufiicient to effect stabilization; however,all or essentially all of the alpha crystals may be converted to thebeta crystal form at high temperatures.

In the present invention, one may use mixtures of the polymorphic dyeswith or without nonpolymorphic types and/or inert solid diluents. Thedye mixture subjected to the process of the present invention shouldcontain no less than of the polymorphic dye, and no single polymorphicdye should constitute more than 90% of the total mixture of dyes. Thedye mixture is stabilized by heating and drying the dye mixture at atemperature of 80 C. or higher but below the melting point of the dyesuntil at least 5% by weight of the polymorphic dye or dyes is convertedto the beta crystalline form.

When the compositions of the present invention are produced in a hotaqueous slurry, stabilization is succussful at a pH as high as 11 whilemaintaining a temperature of about 80 C. or higher prior to isolatingthe dye; a pH of 8 or lower is preferred because the stabilizer:- tionis completed more rapidly. Stabilization has been effemed in thisprocess at a pH as low as 1. Since the stabilization may be completednear the neutral point, the use of a large amount of acid isunnecessary.

The total amount of polymorphic dyes stabilized according to the presentinvention can vary from 30% to 100% of the dye mixture. Also, thereshould be at least 10% of a dilferent dye (or dyes), either polymorphicor nonpolymorphic, in order to assure good solubility in gasoline. Sincethe minimum polymorphic dye content is 30% and at least 5% of thepolymorphic portion must be converted to the beta form, it is clear thatthe minimum beta content of the dye mixture to assure stability is 1.5%.The nonpolymorphic dyes do not cake on storage as there is no transitionof crystal forms and a mixture consisting of essentially less than 30%of polymorphic dyes plus more than 70% of non- (a) Unstabilizeddye.-2-methyl-4-(o-tolylazo)aniline (1 mole) was diazotized in dilute,aqueous hydrochloric acid by the addition of aqueous sodium nitritesolution, in known manner. The cold solution of diazotized intermediatewas coupled to 1.08 moles of beta-naphthol in cold, alkaline, aqueoussolution, in known manner.

The slurry of Sudan IV, l-(4-o-tolylazo-o-tolylazo)- 2-naphthol, thusobtained was made strongly alkaline by the addition of aqueous sodiumhydroxide and heated to about C. to dissolve unreacted beta-naphthol.The slurry of dye was filtered and washed with water until neutral. Thiswet dye was dried for two days by the customary manner in an oven at 50to 55 C., then ground to a fine powder.

The ground dye was a free-flowing, soft powder. When examinedmicroscopically, the dye particles were without apparent regular shape.When examined by of the total weight 'to a strong test on Congo redpaper.

' i 3 X-ray difiraction methods, the powder-was found to be crystalline.The major difiraction maxima, using 'the I characteristic radiation ofcopper (K-alpha line), were I at 5.9, 11.5, 12.8, 18.5, 24:6, 26.6 and28.8 degrees (alpha type of crystal). I

When the dye powder was stored in an accelerated caking test at 60 C.,it caked severely within four days. This dye would be unsuitable forpowder-feedingsystems of-the-eductor type'at gasoline refineries. I I:(b) Stabilized dye.-Another preparation was made as described in part(a) of this example, except that the aqueous,.alkaline dyeslurry at 75C., was not filtered. Instead, it was acidified with aqueoushydrochloric acid The acidic slurry was heated at 95 C. for one-halfhour to promote the desired crytsal change. This slurry of stabilizeddye was made strongly alkaline with aqueous sodium hydroxide toredissolv'e any excess beta-naphthol. The dye was Igltered, washed,dried and ground as described in part The stabilized dye powder hadessentially the same tinctorial strength, shade and solubility ingasoline, also the same melting point, as the unstabilized sample.However, the stabilized sample remained a soft,'freeflowing powder afterstorage for four days at 60 C. followed by two days at 80 C. Also, thisstabilized dye was found to contain only needle-shaped crystalswhi'chgave characteristic, major diffraction maxima with 'X rays, asdescribed, at 10.4, 12.0,13.7, 14.2, 17.9, 20.2, 24.5, 2 5.8, and 28.3degrees (beta type of crystal).

Iheproc'ess of part (b) of this sample was repeatedin a series ofexperiments in which the pH varied in small intervals from 1 toll.Stabilized dye was obtained in all these experiments. In this series,stabilization tests we're inade on samples removedover short intervalsof time and it was found that the conversion to beta forrn, sufficientfor stabilization, was completed in less "than twenty-minutes at all pHvalues below 11. A'tthet'emperature employed (95 C.), the conversion tobeta-form was 100% in less than twenty minutes in all experimentsconducted at a pH of8 or below.

-It is evident that the novel crystalproperties of the stabilizeddyei'mp'arted resistance to 'cakin'g on storage.

EXAMPLE 2 I I (Z1) Unstabilizd klye.4-phenylazo 2, 5-xylidinehydrochloride. (1-mole) was diazotized in dilute, aqueous sulfuric acidmediuin by the addition of aqueous sodium nitrite solution, in knownmanner. The solution of 4- phenylazo-2,5-xylenediazonium sulfate wasadded to a cold, aqueous, alkaline solution of beta-naphthol (1.1 1moles).

The stabilized dye powder had essentially the same tinctorial strength,shade andsolubility in gasoline, also the same melting point, as theunstabilized dye. However, it contained microscopically visible,needle-s .aped

The resulting slurry of red dye, l-(4-phenylazo- 2i5- Vxylyazo)-2-naphthol, was made strongly alkaline with sodium hydroxideand heated to about 75 C. then isolated, dried at 50 to C. and ground asdescribed in Example 1(a).

This dye was initially a free-flowing, soft powder with no regularcrystal form apparent under 1,000 magnification. However, when examinedby X-r'ay methods, this dye was found to be crystalline with majordifir'action maxima 8, 10.8, 11.7, 12.6, 13.6, 15.7, 163,172, 19.1,22.4, 24.0, 24.8, 25.5 and 29.0 degrees (alpha I type).

When this dye powder was stored in an accelerated caking test, it cakedafter two daysat C., followed by. one day at 80 C. After eleven days at80 C., visible needle-shaped crystals had appeared in the 'caked dye.

(b) Stabilized dye-Another preparation was made as in part (a) exceptthat the alkaline slurry of the dye in I alpha I crystal form wasacidified to Congo red paper with hydrochloric acid and heated for onehour at 95 C. The slurry of stabilized dye was made strongly alkalinewith sodium hydroxide and then filtered and worked up as described inExample 1(a).

crystals and aggregates with similarly shaped projections. It remained-'a soft, -free-flowing powder after '2 days storage at 60 (9.,-foll6wed by eleven days at 80 L. The X-ray difiraction maxima of thestabilized dye were diiierent from those as the unstabilized dye. IMafior maxima were found at 6.-2, 816, 10.5, 11.0, 12.5, 1 .4.18.0,3-194, 20.2, 2l.0,'24.-2, 26.0 and 28.0 degrees (beta crystals). III This dye is also obtained in a second metastable crystal form (alphaI- I), apparently depending upon undefined variations in thepreparation, which metastable form can likewise. be stabilized asdescribed above. The X- ray difiraction'maxima of the alpha II form arefound at 6.9, 8.-l,- 1-1.-8, 12.7, 13.6,153, 16.3, 17.3, 19.8, 22.4,23.9, 25.6, 26.3 and 29.2 degrees. I I

;It is evident that the novel crystal properties of the stabilized dyeimparted resistance to caking on storage.

EXAMPLE 3 -iS'idbilizd'izb'n 'bfi'z "fiiz'iiiire -33) me polymorphicdyes "2-m'eih 1-4 -mamynmtamnm (1.40 moles) and 4- phenylazo2,5-xyl-idene hydrochloride (0.68 -mole) were diazotized in an'aqueousmedium of mineral acids by the addition of aqueous sodium nitritesolution, inknown manner. The cold solution of diazonium salts, derivedfrom the two above intermediates, was coupled to 2.2 moles ofbet'a-naphthol, in cold aqueous solution alkaline with 'NaOH, and'heatedto about 50 C. while strongly alkaline. II I I I (a) This slurry erun'stabliized dye was divided; half was filtered and Washed with water,in the usual manner. This 'unstabilized W et dye filtered cake was further diyidedypart was dried inthe usual-manner at 50 to 60 C. for twodays, and another part was dried and stabilized by heatingin an air ovenfor two days at 95 (3., a temperature suificiently high tofuse somecommercial red gasoline dyes based on Sudan -IV because of the presenceof isomersand impurities. I I

I -(b) The remaining hali of the unstabilized, alkaline slurry of dye,While a-t-5060 C. was acidified by adding aqueous hydrochloric-acid toastrong test on Congo redepaper. It wasagitated and heated to 95 C.which temperaturemight be expected to cause'melting and tarring ofordinary commercial dyes, based on Sudan Fill with amixture of otherdyes, since appreciable excess of beta-napht-hol (melting i-point l2- 2C.) is usually present and precipitated-in part by acidification. Thedye slurry Was sampledafter agitation-for 6 minutes'at 9395 C,again-afterBO minutes-and finally after an hour. At this time the main.-portion as Wellas the samples were made strongly alkaline, pH 11-12,with sodium hydroxide, filtered, washed, 'dried at -5 0 'C.-'and ground.

Themain portion 'of the stabilized, acidic dye slurry Was similarlymade, alkaline and washed after filtration.

A part was dried in the normal manner at 50 C. and another part= at-C,-for two days. The dye samples were ground. a

Accelerated (3 daysat 60 C. plus 2 days at 70C.) and-ordinarytemperature f4 months) caking tests, solubility and tintorialproperties. in gasoline, and X-ray difffiactiontests showe'd successfulstabilization by either the high'temp'eratur'e 1'( 95 C.) treatment-ofwet, filtered, un'stbilize'd dye p'ai t (a) or by the hot, acidic slurrytreatment part (b). The only sample not stabilized was the one thatwas'filt'ere dfprior to'a'cid treatment and dried at 50 to 60 2:; Itcakes severely in less than "3 days storage at 60 C.

Tinctorial strengths in-gasolinewere unchanged by the variousstabilization methods.

The unstabiliz'ed dyepowder contained only alpha-type crystals of SudanIV and 1-(4-phenylazo-2,5-xylylazo)- Z-naphthol by X-ray dififractiontest. The heat-stabilized sample contained about 95% of the Sudan 1Vcomponent in beta form and appreciable amounts of both alpha and betacrystals of the other dye. All of the acid slurried samples contained atleast 5% of the dye in beta form.

A similar sample of wet dye, dried and stabilized at 116 C. for twodays, was similarly stable.

EXAMPLE 4 Stabilization polymorphic dyes in mixtures with nonpolymorphicdyes in the absence or presence of colorless diluents (a) Onepolymorphic dye and one non-polymorphic dye-A mixture was preparedcontaining the alpha or unstable form of Sudan 1 and the stablenonpolymorphic dye, 1 [442,3-xylylazo)-2,5-xylylazo]-2-napl1- thol asfollows:

2-methyl-4-(o-tolylazo)aniline was mixed with 4-(2,3- xylyazo) 2,5-xylidine hydrochloride in approximately 75 :25 molar ratio (total 1mole). This mixture of amines was diazotized in known manner in dilute,aqueous hydrochloiic acid medium by the addition of aqueous sodiumnitrite solution. The cold solution of diazotized intermediates wascoupled in known manner with 1.05 moles of beta-naphthol in a cold,aqueous solution made alkaline with NaOH.

This alkaline slurry of water-insoluble dyes was heated to about 50 C. Apart was filtered, washed with water, dried at 5 0 to 55 C. and ground.

Another part or the dye slurry was stabilized by the addition ofhydrochloric acid and heating at 95 C. for 1 hour as described for SudanIV in Example 1(b). The slurry of stabilized dye was made alkaline withsodium hydroxide, filtered, washed, dried at 50 to 55 C. and ground.

Comparison of the two dye powders was made by X-ray diffractionexamination and by accelerated caking tests.

The first sample obtained from the alkaline slurry was unstabilized andcontained only the alpha crystals of Sudan IV and crystals ofl-[4'(2,3-xylylazo)-2,5-xylylazo] -2-naphthol. It caked on acceleratedtesting at 60 and 80 C.

The mixture that was stabilized by acid treatment was found to containboth alpha and beta crystal forms of Sudan 1V and crystals of theaccompanying dye. The powder remained a free-flowing material afterexposure to temperatures of 60 and 80 C., as described in Exampie 1.

(b) Two polymorphic dyes and one nonpolymorphic dye-A mixture of 0.3mole of 2-methyl-4-(o-tolylazo)- aniline, 0.1 mole of4-phenylazo-2,5-xylidine hydrochloride and 0.6 mole of4-phenylazo-2,3-xylidine hydrochloride [the latter was made in knownmanner by coupling benzenediazonium chloride to the omega sulfonicderivative of 2,3-xylidine and then hydrolyzing in alkaline medium toregenerate the free amino group of the 4- phenylazo-2,3-xylidine] wasdiazotized in known manher in dilute, aqueous hydrochloric acid mediumby the addition of aqueous sodium nitrite solution. These diazoriediates were coupled with 1.1 moles of beta-naphdilute aqueous NaOHsolution to which had been aded 20% by weight (calculated on final dyes)of powdered, water-insoluble, gasoline-soluble organic polymer. Thepolymer was cumar resin (trademark of Barrett -Div., Allied ChemicalDyes Corp.see The Condensed Chemical Dictionary, Francis M. Turner, EdDir., 4th Ed, 1950, page 200), a synthetic resin mixture of polymerizedcoumarone, indene and associated coaltar compounds. The alkaline slurryof the polymer and three dyes was divided into two parts. One part wasfiltered at 50 C. washed alkali-free, dried at 50 to 55 C. and ground.The other part was stabilized by following the acidic treatmentdescribed in part (a) of this example. The two samples were compared byX-ray difiraction and by accelerated caking tests. The stabilized samplecontained about 5% of beta crystals of Sudan IV andl-(4-phenylazo-2,5-xylylazo)-2-naphthol and did not cake on storage atelevated temperatures. By contrast, the unstabilized sample caked in thesame storage test (3 days at 70 C. and 3 days at C.) and no betacrystals were detected in the X-ray analysis. The polymorphic dyes werepresent as alpha crystals and the nonpolymorphic dye,1-(4-phenylazo-2,3-xylylazo)- Z-naphthol, was present in crystallineform along with particles of the amorphous polymer.

The same results were obtained when the experiment was repeated exceptthat the polymer was not added to the coupling reaction mass, but Wasground into the isolated dye powders following their respectivetreatments but prior to tests for stability.

EXAMPLE 5 Stabilization of polymorphic dye mixtures Mixtures of2-methyl-4-(o-tolylazo)aniline and 4- phenylazo-2,5-xylidinehydrochloride were diazotized and coupled to an excess of beta-naphtholby the methods described at the beginning of Example 3. The ratio of thetwo polymorphic dyes thus obtained; Sudan IV to1-(4-phenylazo-2,5-xylylazo)-2-naphthol, was 25:75 in one series ofsamples and 50:50 in a second series of samples. The dye mixtures weredivided and treated, as described in Example 3, except that the samplesstabilized by high temperature drying were held at 100 C. for 16 to 20hours and that those stabilized by the hot acidic slurry method wereagitated at to C. for 4 hours.

The degree of conversion from the unstable alpha crystal form to thestable beta form, for each dye in this mixture, is shown as follows:

Dye ASudan IV or l-(4-o-tolylazo-o-tolylazo)-Z- naphthol. DyeB-l-(4-phenylazo 2,5-xylylazo-2-naphthol.

25:75 MIXTURE Storage stability tests were conducted for 3 days at 60C., then 4 days at 70 C., then 3 days at 80 C. All samples containingbeta crystals were stable, the others caked at 60 C. Thus, the relativeamounts of the two polymorphic dyes can be changed without aiiecting thesuccessful stabilization of the dye mixtures by either method.

EXAMPLE 6 Stabilization of "Sudan IV powders Powdered alpha crystals ofSudan IV (1 part) prepared as described in Example 1(a) and containingless than one percent of beta-naphthol were agitated in 16 parts ofwater, alkaline to Clayton yellow paper with tolylazo-LS-xylyl-azo.).-2-naphthol. v y heated to 60 C., the dye was filtered ofi, washed,dried l sodium hy'droxide, shortened to 60" C. Hydrochloric acid 'Wasadded until a blue test was observed on Congo red paper, and the slurrywas-heated to 95 C. for'tw'o hours. After "realkali'zing to Claytonyellow paper test with sodium hydroxide, the 'dye was filtered, washed,and dried iortwodays at 60 Cami ground. 7

Accelerated baking tests showed that the dye was nonc'aking after 3days'at60 C., followed by 3.5 days at 70 C. X-ray examination "showedonly beta crystals of t dye This test illustrates that Sudan IV can bestabilized by the hot-acidic-slur'ry method after the dye has beenobtained as the "alpha crystals in form.

EXAMPLE 7 One mole of 4-(o-tolylazo)-2,5 Xylidine, (prepared in knownmanner by coupling diazotizedo-toluidine to 2,5- XyIidine') wasdiazotized in dilute, aqueous hydrochloric acid medium by the additionof aqueoussodium nitrite solution. The resulting solution of thediazonium chloride was coupled to '1 Tnole of beta-naphthol in cold NaOHsolution to give an alkaline slurry of 1-(4-0- The dye slurry was at 50fto 60 and ground.

Prolonged storage of thisunstable dye .powder showed baking atnormaltemperatures.

Part of this unstable dye powder (alpha crystals) was recrystallizedfrom benzene and air dried at room temperature to produce the stablebeta crystal form, v -Anotherpart was stabilized byheating at 100 C. fortwo days and re'grinding. 4

Another portion was stabilized by slurrying 6 parts of thepowdered alphacrystals with 94 parts of water, al-

kalizing with sodium hydroxide to Clayton yellow paper 'test, heating to60 C., acidifying with hydrochloric acid toCongo red paper test, andheating at 90;to 95 C. fo'rtwo hours. .Then the dye slurry was madealkaline to Clayton yellow paper test with sodium hydroxide, the dye wasfiltered oif, Washed, dried at 60 C., and ground. Whenthe last three dyepowders were examined by X-ray and subjected to accelerated cakingtests, -'it was clear that all of them had been stabilized and convertedto beta type crystals.

The unstable powder, examined by the X-ray diftrac- 1 tion methoddescribed in Example 1 was found to be prystalline with the highermaxima at 5.9, 11.3, 13.0, 18.7, 24.5-24.7, 26.6 and 28.9 (alpha type).

Similarly examined, the stabilized dye samples were crystalline with thehigher maxima at 10.4, 11.9, 13.7, 18.0, 20.0, -23.4, 24.4, 25.6 and28.2 degrees (beta type).

EXAMPLE 8 One mole of 4-(2,4-Xyiylazo) 2,5-xylidine, (prepared in knownmanner by coupling diazotized 2,4-xylidine to 2,5-xylidine) wasdiazotized and coupled in'dilute NaOl-l solution to 1.1 moles ofbeta-naphthol. The alkaline slurry of +1-[t-(2,4-xylylazo)2,5-Xylylazo]-2-naphthol was heated to 60 C., the dyewas filtered on, washed,

dried at 50 to 60 C. and ground.

Prolonged storage of this unstable dye powder showed caking at normaltemperatures.

'Whenthis dye was treated by the three stabilization methods describedin Ex'ample7 stabilized samples were obtained as shown by acceleratedbaking tests and by X-ray diifraction examination. The unstable dye wasfound to hem alpha crystalline form. The crystals obtained from be "onewere entirely in beta form, and those obtained in the high temperaturedrying and acid slurry treatments were mostly alpha mixed with some betacrystals.

' The X-ray difiraction 'maxima, as determined 'by meth- OdS of Example1, WC161'5.9, 11.4, 12.9, 18.7, 24.4, 26.5 and 28.7 degrees (alphatype); and 10.3, 11.8, 131.5, 17L8, 20.2,243, 25:6,and 28.1'degrees(beta type).

8 V EXAMPLE 9 Que gram-mole of Sudan III,l-(psphenyl'azophenylazo)-2-naphthol, was prepared from diazotizedp-phenylazoaniline and an aqueous, alkaline solution of beta naphthol,in known manner. The slurry of dye was heated to about 60 C. anddivided.

One .part of the slurry was filtered and the dye was washed alkali-tree.A "part of this wet dye filter cake was dried at C. for 4 days, andanother part was stabilized by drying at 905C; io'rtwo days. Bothsamples were. ground to soft powders.

Another part of the dye slurrywas acidified'with hydrochloric acid to astrong test on Congo red paper and then heated at 95 C. for one hour.This slurry of stabilized dye was :realkalized with sodium hydroxide toa test on Clayton yellow paper, filtered, and the dye was Washedalkali-free. Part of this stabilized wet dye was dried at 50 C. for 4days and another part at 90 C. for 2 days. Both samples were ground topowders.

Accelerated caking tests showed that all of the stabilized samples weresoft, tree-flowing powders after storage for 6 .days at C. and 4 moredays at C., while the untreated sample acaked after the same exposureand changed color (as "a powder) from red to a brownish red color. Otherproperties of the samples were equal, e.g., huein gasoline, meltingpoint, an'dtino torial strength in gasoline solution.

X-ray powder diitraction tests showed that the stabilized samplescontained alpha 1,, alpha .11 and beta crystals whereas theunstabiliz'edasample was entirely in the alpha I form.

The alphaH, metastable crystal can beobtained by recrystallization fromglacial acetic acid, whereas the normal alpha I metastable crystalresults irom ordinary aqueous manufacture or recrystalhzaticm frombenzene.

The major maxima by X-ray diffraction examination are: (1) alpha I typeat 6.5, 7.4, 9.1, 10.0, 12.0, 12.8, 13.2, 13.7, 15.5, 16.2 and 26.6degrees; (2) alpha II type at 5.1, 7.8, 12.8, 14.6, 15.6, 16.3 and 18.6degrees; and (3) beta type at 11.4, 13.6, 18.9, 19.9, 20.2, 21.8, 24.7,26.2, 27.0}282, 2.9.0 and 3458 degrees. Anarnbr phou's form can beobtained by solution and precipitation from sulfuric acid.

The polymorphic dyes-describedlin Examples 7, 8 and 9 may be utilizedand stabilized in mixtures according to the present invention.

In the present high temperature drying process, it has been found thatthe polymorphic dyes can be stabilized against caking on storage'whenabout 5% or more of the alpha form has been converted to beta form. Thiscondition is satisfied when the alkaline-extracted samples of the dyesare heated between C. and their melting points for a period of timeranging from about 15 to 50 hours. As a rule the minimum conditionstherefore, are about 80 C. and 15 hours, or until atleast 5% of thealpha form has beenconverted to beta form.

As many apparently widely difierent embodiments of this invention may bemade without departingfrom the spirit and scope thereof, it is to beunderstood that this invention is -notlirnited to the specificembodiments thereof except as defined in the appended claims.

The-embodiments of the invention in whicb an exclusive propertyorlprivllege -:is claimed are defined 'as follows.

I claim:

1. A process tot-preparing agasoline-s'oluble and freeflowing stabilizedcrystalline disazo dye powdermixture, in which process atleast twopolymorphic dyes in their unstable crystalline form and taken irorn thegroup consisting of (a) l-(pzphenlazophenylazo)-2-napl1thol, (b)

1-(4-oatolylazo-o-tolylazo)-2-naphthol, (c) 1-(4-phenylazo-2,5-xylylaz0)-2-naphthol, (d) 1-(4-o-tolylazo-2,5-XylylaZo)-2-naphthol,(e) l-[4-(2,4-xylylazo)-2,5 xylylazo]- 2-naphthol, in such proportionthat-one of said dyes is present in an amount up-to by Weight of themixture, are heated, under anhydrous conditions, at about 80 C. to belowthe melting temperature of said dyes for a period of from about 15 to 50hours to convert at least by Weight of the original dye mixture to thestable beta-crystalline form, said beta-crystalline form of dye (a)having beta X-ray diffraction maxima at 11.4, 13.6, 18.9, 19.9, 20.2,21.8, 24.7, 26.2, 27.0, 28.2, 29.0 and 34.8 degrees, saidbeta-crystalline form of dye (b) having beta X-ray difiraction maxirnaat 10.4, 12.0, 13.7, 14.2, 17.9, 20.2, 24.5, 25.8 and 28.3 degrees, saidbeta-crystalline form of dye (c) having beta X-ray didraction rnaxima at6.2, 8.6, 10.5, 11.0, 12.5, 17.2, 18.0, 19.4, 20.2, 21.0, 24.2, 26.0 and28.0 degrees, said beta-crystalline form of dye (d) having beta X-raydifiraction maxima at 10.4, 11.9, 13.7, 18.0, 20.0, 23.4, 24.4, 25.6 and28.2 degrees, said beta-crystalline form of dye (e) having beta X-raydifiraction maxima at 10.3, 11.8, 13.5, 17.8, 20.2, 24.3, 25.6 and 28.1degrees, followed by recovering and grinding said stabilized mixture.

2. A process for preparing a gasoline-soluble and freefiowing stabilizedcrystalline disazo dye powder mixture, in which process at least twopolymorphic dyes in their unstable crystalline form and taken from thegroup consisting of (a) l-(p-phenylazophenylazo)-2-naphthol, (b)1-(4-o-tolylazo-o-tolylazo)-2-naphthol, (c) 1-(4-phenylaZo-2,5-Xylylazo)-2-naphthol, (d l(4-o-tolylazo-2,5-Xylylazo)-2-naphthol, (e)1-[4-(2,4-xylyiazo)-2,5-Xylylazo]- 2-naphthol, in such proportion thatone of said dyes is present in an amount up to 90% by weight of themixture, are heated at about 85 to 100 C. in an aqueous slurry thereofat a pH not more than 11 for a period of from sh; minutes to two hoursto convert at least 5% by weight of the original dye mixture isconverted to the stable beta-crystalline form, said beta-crystallineform of dye (a) having beta X-ray diffraction mariima at 11.4, 13.6,18.9, 19.9, 20.2, 21.8, 24.7, 26.2, 27.0, 28.2, 29.0 and 34.8 degrees,said beta-crystailine form of dye (b) having beta X-ray diffractionmaxiina at 10.4, 12.0, 13.7, 14.2, 17.9, 20.2, 24.5, 25.8 and 28.3degrees, said betacrystflline form of dye (0) having beta Y-raydiffraction maxima at 6.2, 8.6, 10.5, 11.0, 12.5, 17.2, 18.0, 19.4,20.2, 21.0, 24.2, 26.0 and 28.0 degrees, said beta-crystalline form ofdye (d having beta X-ray diitraction maxima at 10.4, 11.9, 13.7, 18.0,20.0, 23.4, 24.4, 25.6 and 28.2 degees, said beta-crystalline form ofdye (e) having beta X-ray diffraction maxima at 10.3, 11.8, 13.5, 17.8,20.2, 24.3, 25.6 and 28.1 degrees, followed by recovering, drying andgrinding said stabilized mixture.

3. The process of claim 2 maintained at a pH Within the range of 3 to 8.

References Qited in the file of this patent UNITED STATES E ATENTS1,986,116 Payne Ian. 1, 1935 2,007,386 Stanley et al. July 9, 19352,124,590 Reed July 26, 1938 OTHER REFERENCES Colour Index, 2nd Edition,volume 3, 1956, page 3207.

1. A PROCESS FOR PREPARING A GASOLINE-SOLUBLE AND FREEFLOWING STABILIZEDCRYSTALLINE DISAZO DYE POWDER MIXTURE, IN WHICH PROCESS AT LEAST TWOPOLYMORPHIC DYES IN THEIR UNSTABLE CRYSTALLINE FORM AND TAKEN FROM THEGROUP CONSISTING OF (A) 1-(P-PHENLAZOPHENYLAZO) -2-NAPHTHOL, (B)1-(4-O-TOLYLAZO-O-TOLYLAZO)-2-NAPHTHOL, (C)1-(4-PHENYLAZO-2,5-XYLYLAZO)-2-NAPHTHOL, (D)1-(4-O-TOLYLAZO-2,5-XYLYLAZO)-2-NAPHTHOL, (E)1-(4(2,4-XYLYLAZO)-2,5-XYLYLAZO)2-NAPHTHOL, IN SUCH PROPORTION THAT ONEOF SAID DYES IS PRESENT IN AN AMOUNT UP TO 90% BY WEIGHT OF THE MIXTURE,ARE HEATED, UNDER ANHYDROUS CONDITIONS, AT ABOUT 80*C. TO BELOW THEMELTING TEMPERATURE OF SAID DYES FOR A PERIOD OF FROM ABOUT 15 TO 50HOURS TO CONVERT AT LEAST 5% BY WEIGHT OF THE ORIGINAL DYE MIXTURE TOTHE STABLE BETA-CRYSTALLINE FORM, SAID BETA-CRYSTALLINE FORM OF DYE (A)HAVING BETA X-RAY DIFFRACTION MAXIMA AT 11.4, 13.6, 18.9, 19.9, 20.2,21.8, 24.7, 26.2, 27.0, 28.2, 29.0 AND 34.8 DEGREES, SAIDBETA-CRYSTALLINE FORM OF DYE (B) HAVING BETA X-RAY DIFFRACTION MAXIMA AT10.4, 12.0, 13.7, 14.2, 17.9, 20.2, 24.5, 25.8 AND 28.3 DEGREES, SAIDBETA-CRYSTALLINE FORM OF DYE (C) HAVING BETA X-RAY DIFFRACTION MAXIMA AT6.2, 8.6, 10.5, 11.0, 12.5, 17.2, 18.0, 19.4, 20.2, 21.0, 24.2, 26.0 AND28.0 DEGREES, SAID BETA-CRYSTALLINE FORM OF DYE (D) HAVING BETA X-RAYDIFFRACTION MAXIMA AT 10.4, 11.9, 13.7, 18.0, 20.0, 23.4, 24.4, 25.6 AND28.2 DEGREES, SAID BETA-CRYSTALLINE FORM OF DYE (E) HAVING BETA X-RAYDIFFRACTION MAXIMA AT 10.3, 11.8, 13.5, 19.8, 20.2, 24.3, 25.6 AND 28.1DEGREES, FOLLOWED BY RECOVERING AND GRINDING SAID STABILIZED MIXTURE.